Bone loss, traditional diet, and cold adaptation in Arctic populations.

North American Inuit and Inupiat ("Eskimo") populations have been described as having a lower bone mass relative to Caucasians as a consequence of their traditional high-protein "acid-ash" diet. However, this bone buffering mechanism has also been implicated as a risk factor for osteoporosis in industrialized Caucasian populations, and one recent study has found a positive association between dietary protein, and bone mass in premenopausal women. The original studies documenting the Eskimo-Caucasian difference in aging bone loss do not consider the consequences of population variation in body composition, in particular lean body mass (LBM), which correlates with bone mass. The possibility also exists that the original reference sample may be exceptional rather than normative for bone mineral density (BMD). Regression analysis was conducted on published age- and sex-specific cohort means for BMD, and bone mineral content adjusted for estimates of LBM for the original Eskimo-Caucasian comparisons, and for an additional Caucasian sample from Belgium. Significant differences were found between all groups, including Belgians, and the Wisconsin sample for BMD, supporting the notion of the latter having exceptional bone quality when measured as BMD. When adjusted for LBM, the Eskimo samples are distinct in pattern and magnitude of aging bone loss relative to Caucasians, supporting the hypothesis of real inter-population differences. However, given the current ambiguity surrounding the "protein-calcium buffering" model, an alternative explanation is offered. It is hypothesized that the accelerated bone loss among the Inuit and Inupiat reflects higher production and utilization of the thyroid hormones, T and T , as a mechanism of cold adaptation through enhanced nonshivering thermogenesis. Am. J. Hum. Biol. 9:329-341, 1997. © 1997 Wiley-Liss, Inc.